Lecture 9 - Microbial Genetics Flashcards
4 different levels of genetic study
organism level
cell level
chromosome level
molecular level
the sum of all types of genes constituting an organism’s distinctive genetic makeup
genotypes
the expression of the genotype that creates certain structures or functions
phenotype
where is DNA found in microorganisms?
cells
- eukaryote
- prokaryote
- viruses
basic unit of DNA is
nucleotide
each nucleotide is composed of: (3)
- phosphate
- deoxyribose sugar
- nitrogenous base
two types of nitrogenous bases
purines and pyrimidines
adenine pairs with
thymine
guanine pairs with
cytosine
original parental DNA strand
template strand
DNA goes under what type of replication
semiconservative replication
where is the origin of replication for DNA?
short sequence rich in adenine and thymine bases that are held together by only two hydrogen bonds. (TATA box)
because the origin of replication is AT-rich, ——– energy is required to separate the two strands than would be required if the origin were rich in G and C.
less energy
unwind the DNA helix
topoisomerase
unzips the DNA heliz
helicases
DNA replication - figure 9.6
synthesizing an RNA primer
primase
adding bases to the new DNA chain; proofreading the chain for mistakes
DNA polymerases III
removing primer, closing gaps, repairing mismatches
DNA polymerase I
final binding of nicks in DNA during synthesis and repair
ligase
making single-stranded DNA breaks to relieve supercoiling at origin
topoisomerase I
making double stranded DNA breaks to remove supercoiling ahead of origin and separate replicated daughter DNA molecules
topoisomerase II and IV
figure 9.7
DNA is used to synthesize RNA
transcription
RNA used to produce proteins
translation
transcription figure 9.12
translation figure 9.15
Drugs that inhibit protein synthesis:
rifamycins
actionomycin D
Drugs that interfere with the ribosome:
Erythromycin
Spectinomycin
Chloramphenicol
Aminoglycosides
- Found only in bacteria and archaea
- Coordinated set of genes regulated as a single unit
- Can be inducible or repressible
- Categories determined by how transcription is affected by the environment surrounding the cell
operons
- Catabolic operons; operons encoding enzymes that act in catabolism
- Operon is turned on (induced) by the substrate(s) for which the structural genes encode
- Enzymes needed to metabolize a nutrient are only present when that nutrient is present in the environment
inducible operons
- Contain genes coding for anabolic enzymes
- Several genes in a series are turned off (repressed) by the product synthesized by the enzyme
repressible operons
3 features of the lac operon
- regulator
- control locus
- structural locus
composed of the gene that codes for the repressor, a protein capable of repressing the operon
regulator
two parts of the control locus
promoter and operator
recognized by RNA polymerase
promoter
acts as an on/off switch for transcription
operator
made up of three genes, each coding for a different enzyme needed to catabolize lactose
structural locus
figure 19.8
Lac Operon Regulates Genes Based on Lactose Availability
—-???
usually in the on mode
repressible operons
Will only be turned off when the nutrient is no longer required
repressible operons
serves as a corepressor to block the action of the operon
excess nutrient
figure 9.19
what type of cells do not have operons
eukaryotic cells
together these interact with the promoter
enhancer and mediator
- Regulate gene expression for thousands of bp away
- Position independent
- DNA between enhancer and promoter loops out so that enhancer proteins can interact with proteins bound to the promoter
enhancer
- Large complex of proteins that mediate interaction between enhancer binding proteins and general transcription factors at the promoter
mediator
An event in which one bacterium donates DNA to another bacterium
recombination
what is the end result of recombination
a strain different from both the donor and recipient strain
extrachromosomal DNA adept at moving between cells
plasmids
any organism that contains and expresses genes that originated in another organism
recombinant
Any transfer of DNA that results in organisms acquiring new genes that did not come directly from parent organisms
horizontal gene transfer
three types of horizontal gene transfer in bacteria
conjugation
transformation
transduction
- A mode of genetic exchange in which a plasmid or other genetic material is transferred from a donor to a recipient cell via a direct connection
- Can occur in both gram-positive and gram-negative cells
conjugation
figure 9.20
- Bear genes for resisting antibiotics or other drugs
- Commonly shared among bacteria through conjugation
- Can confer multiple resistance to antibiotics
- R factors can also carry genetic codes for resistance to heavy metals, or synthesizing virulence factors
resistance plasmids or factors
The acceptance by a bacterial cell of small fragments of soluble DNA from the surrounding environment
transformation
cells that are capable of accepting genetic material through transformation
competent
figure 9.22
- The process by which bacteriophage serve as a carrier of DNA from a donor cell to a recipient cell
- Occurs in a broad spectrum of bacteria
- The participating bacteria in a single transduction event must be the same species
transduction
- Random fragments of disintegrating host DNA are taken up by a phage during assembly
- Any gene from the bacterium can be transmitted
generalized transduction
figure 9.23
Transposable Elements - shifting segments of the genome
TE exists as a small DNA piece in genome
TE can change location (jump)
TE can replicate itself
The TE could insert into a plasmid and be transferred to other bacteria
The smallest TEs consist only of two tandem repeats
insertion elements
A type of TE that can transcribe DNA into RNA and then back into DNA for insertion in a new location
retrotransposon
Other TEs contain genes that code for
antibiotic or toxin production
Effects of TEs in bacteria:
- Changes in colony morphology, pigmentation, and antigenic characteristics
- Replacement of damaged DNA
- Intermicrobial transfer of drug resistance
The E. coli tet operon was originally identified as a _____ that confers resistance to the antibiotic tetracycline.
transposon (Tn10)
bind to the operator of the tetracycline-resistance operon – similar to how the lac operon works
TetR protein
- Have the ability to make their hosts pathogenic.
- Contain multiple genes that are coordinated to create a new trait on the bacterium
- Islands flanked by sequences that look like genes for TE enzymes
pathogenicity islands
Any change to the nucleotide sequence in the genome
The driving force of evolution
mutation
A microorganism that exhibits a natural, nonmutated characteristic
The trait present in the highest numbers in a population
wild type
an organism that bears a mutation
mutant strain
A random change in the DNA arising from errors in replication that occur randomly
spontaneous mutation
result from exposure to known mutagens
induced mutations
Small mutations that affect only a single base on a gene
Involve addition, deletion, or substitution of single bases
point mutations
mutations that lead to cell dysfunction or death
lethal mutation
produce neither adverse honor helpful changes
neutral mutation
Any change in the code that leads to placement of a different amino acids
missense mutation
Changes a normal codon into a stop codon that does not code for amino acid
nonsense mutation
Alters a base, but does not change the amino acid and has no effect
The redundancy of the code assures that certain amino acids will not be altered by a change in the third base of the codon
silent mutation
occurs when a gee that has undergone a mutation reverses to its original
back mutation
Occurs when one or more bases are inserted into or deleted from a newly synthesized DNA strand
frameshift mutation
This alters the reading frame of the mRNA
Nearly always result in a nonfunctional protein
Every amino acid after the mutation is different from what is coded for in the original DNA
Insertion of bases in multiples of three does not disturb the reading frame
frameshift mutation
Repair of damage caused by ultraviolet radiation
photoreactivation
Mutations are excised by a series of enzymes that remove the incorrect bases and add the correct ones
excision repair
Repair of damage caused by ultraviolet radiation
photoreactivation
Mutations are excised by a series of enzymes that remove the incorrect bases and add the correct ones
excision repair
- A repair system can locate mismatched bases that were missed during proofreading
- The base must be replaced soon after the mismatch is made, or it will not be recognized by the repair enzymes
mismatch repair
Commonly used to rapidly detect chemicals with carcinogenic potential
ames test
not repaired, permanent and heritable
mutations